Bone fixation assembly

ABSTRACT

A bone fixation system includes at least one bone fixation member and a bone fixation instrument. The bone fixation member includes a strap and a locking mechanism. The strap can be pulled through the locking mechanism so as to form a loop about a target bone so as to secure first and second bone segments in an approximated, compressed configuration. The bone fixation instrument is configured to apply tension to the loop about the target bone. The fixation instrument includes a tension assembly that is configured to secure a free end of the bone fixation member to the fixation instrument. The tension assembly is further configured to pull the free end so as to increase tension in the loop while the tension in the loop is less than a select tension. The tension assembly is unable to further increase tension in the bone fixation member once the tension in the bone fixation member has reached the select tension. The fixation instrument further includes a cutter assembly that is configured to cut the free end of the bone fixation member so as to separate the free end from the loop.

BACKGROUND

In order to provide access to certain internal anatomy, such as the heart during an open heart procedures, midline sternotomies are typically performed. A midline sternotomy creates a cut substantially along the midline of the sternum, thereby dividing the ribcage into two halves and allowing the surgeon to move the ribcage so as to provide access to the heart. Upon completion of the open heart procedure, it is desired to approximate and compress the sternum, and rigidly maintain the sternal halves in their approximated position relative to each other so that the sterna halves are prevented from moving with respect to each other to promote bone fusion in the weeks following the surgical procedure.

During normal anatomical function, for instance during respiration, body movement, and carrying of objects, forces can be generated that act on the sternum. One conventional system sternal fixation assembly includes stainless steel wires that are placed either parasternally (around the sternum) or transsternally (through the sternum bone) using a cutting needle that is attached to the wire, and subsequently twisted to tighten the wire against the sternum. However, the twisting generates tensile forces onto the wires that tend to weaken the wire, which can result in breakage both during the closure or post-operatively. Furthermore, this type of system relies on the experience of the surgeon when tightening the wires. If the wires are not tightened enough, the sternal compression can be compromised. If the wires are tightened too much, the wire can cut into or through the sternum and/or can break.

SUMMARY

In accordance with one embodiment, a bone fixation instrument is configured to apply tension to a bone fixation member so as to tighten the bone fixation member about a target bone. The bone fixation instrument includes a body that defines a front end and an opposed rear end, a grip configured to secure a free end of the fixation member to the fixation instrument, a traveler that is connected to the grip such that the grip moves rearward along with the traveler so as to increase tension in the bone fixation member, and an actuator operatively coupled to the traveler. The actuator can be configured to move from an initial position toward a tension position in response to an applied force, thereby biasing the traveler to move rearward. The bone fixation instrument can further include a tension limiter connected between the actuator and the traveler. The tension limiter allows the traveler to move rearward when the tension in the bone fixation member is less than the selected tension, and prevents the traveler from moving rearward when the tension in the bone fixation member reaches the selected tension.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description of the preferred embodiments of the application, will be better understood when read in conjunction with the appended drawings. For the purposes of illustrating the present disclosure, there is shown in the drawings preferred embodiments. It should be understood, however, that the application is not limited to the specific embodiments and methods disclosed, and reference is made to the claims for that purpose. In the drawings:

FIG. 1 is a perspective view of a bone fixation instrument constructed in accordance with one embodiment;

FIG. 2A is a perspective view of a bone fixation member including a body and a locking member, showing the bone fixation member in an initial configuration;

FIG. 2B is an enlarged perspective view of a portion of the bone fixation member illustrated in FIG. 2A, showing the body inserted through the locking member so as to secure the bone fixation member about an underlying bone;

FIG. 3A is a perspective view of a plurality of the bone fixation members illustrated in FIG. 2A shown tightened about a target bone and cut;

FIG. 3B is a perspective view of the bone fixation instrument illustrated in FIG. 1 operatively coupled to and tightening one of a plurality of the bone fixation members illustrated in FIG. 3A;

FIG. 3C is a perspective view of the bone fixation instrument illustrated in FIG. 1 operatively coupled to and cutting one of the tightened bone fixation members illustrated in FIG. 3B;

FIG. 4 is a perspective view of the bone fixation instrument illustrated in FIG. 1, with portions removed to illustrate internal components including a tension assembly and a cutter assembly;

FIG. 5A is a perspective view of the bone fixation instrument illustrated in FIG. 4, showing the cutter assembly in a cutting position;

FIG. 5B is a perspective view of a front end of the bone fixation instrument as illustrated in FIG. 5A;

FIG. 6 is a perspective view of a rear end of the bone fixation instrument illustrated in FIG. 4;

FIG. 7A is a perspective view of the front end of the bone fixation instrument illustrated in FIG. 4, showing the tension assembly in a disengaged position;

FIG. 7B is a perspective view of the distal end of the bone fixation instrument illustrated in FIG. 7A having portions removed and showing the tension assembly in an engaged position;

FIG. 8A is a side elevation view of the bone fixation system, including the bone fixation instrument illustrated in FIG. 4 showing the bone fixation member as illustrated in FIG. 3A, with the target bone removed for the purposes of illustration, shown loosely received in the bone fixation instrument with the tension assembly in the disengaged position;

FIG. 8B is a side elevation view of the bone fixation system illustrated in FIG. 8A, showing the tension assembly in the engaged position such that the bone fixation instrument is secured to the bone fixation member;

FIG. 8C is a side elevation view of the bone fixation system illustrated in FIG. 8B, showing the tension assembly in a tightened position;

FIG. 8D is a side elevation view of the bone fixation system illustrated in FIG. 8C, showing the tension assembly in a disengaged position after having been previously in the tightening position FIG. 8C;

FIG. 8E is a side elevation view of the bone fixation system illustrated in FIG. 8D, showing the operation of a tension limiter whereby actuation of the tension assembly toward the tightened position does not tighten the received bone fixation member;

FIG. 9 is a side elevation view of the bone fixation system illustrated in FIG. 8D, but showing actuation of the cutter assembly; and

FIG. 10 is a perspective view of a bone fixation instrument similar to the bone fixation instrument illustrated in FIG. 4, but constructed in accordance with an alternative embodiment.

DETAILED DESCRIPTION

Certain terminology is used in the following description for convenience only and is not limiting. The words “right”, “left”, “lower” and “upper” designate directions in the drawings to which reference is made. The words “proximally” and “distally” refer to directions toward and away from, respectively, the surgeon using the surgical instrument. The words, “anterior”, “posterior”, “superior”, “inferior” and related words and/or phrases designate preferred positions and orientations in the human body to which reference is made and are not meant to be limiting. The terminology includes the above-listed words, derivatives thereof and words of similar import.

Referring to FIGS. 1-3B, a bone fixation assembly 20 includes a bone fixation instrument 22 and at least one bone fixation member 24 such as a plurality of bone fixation members 24 that are configured to secure a first and second bone segments 26 a and 26 b of a target bone 28, such as a sternum, that are separated at a fracture location 30 together in a compressed approximated position.

In accordance with the illustrated embodiment, each bone fixation member 24 can be substantially configured as a cable tie, and can include a flexible strap 32 defines a strap body 33 and has first end 34 a and a second end 34 b opposite the first end 34 a along the length of the strap 32, a needle tip 36 that extends from the first end 34 a, and a locking mechanism 38 that extends from the second end 34 b. The strap 32 can be made from any suitable biocompatible material as desired, such as PEEK.

Each bone fixation member 24 can further include a first initiation region 40 that extends from the first end 34 a toward the second end 34 b along a portion of a length of the strap 32 (for instance, approximately ⅓ the length of the strap 32) and a second locking region 42 that extends between the first initiation region 40 and the second end 34 b. In accordance with the illustrated embodiment, the second locking region 42 extends from the first initiation region 40 to the second end 34 b. The first initiation region 40 can include a plurality of small protrusions that extend out from the strap body 33 and alternate with recessed regions disposed between adjacent protrusions. Alternatively, the initiation region 40 can be substantially smooth and devoid of protrusions or teeth. The second locking region 42 can include a plurality of locking teeth 48 that extend out from the strap body 33 a distance greater than the protrusions and are separated by recessed regions 51 disposed between adjacent locking teeth. It should be appreciated that the locking region 42 can extend along any portion up to all of the strap body 33 as desired.

The locking mechanism 38 includes a housing 50 a strap receiving slot 52 that extends through the housing 50 and is configured to receive the first end 34 a of the strap 32. In accordance with the illustrated embodiment, the first end 34 a is inserted through the slot 52 so as to define a loop 55 about the target bone 28. The locking mechanism 38 is configured to allow the strap 32 to translate unidirectionally through the slot 52 along the direction of Arrow A so as to reduce the size of the loop 55 about the first and second segments 26 a and 26 b of the target bone 28. For instance, the needle tip 36 can be inserted through the slot 52 and subsequently removed, for instance by cutting a neck 56 of the strap body 33 that defines reduced thickness at a location adjacent the needle tip 36, such that the strap 32 remains in the slot 52. In accordance with the illustrated embodiment, the locking mechanism 38 includes a locking member such as a tongue 54 that is connected to the housing 50 and includes at least one complementary tooth such as a plurality of locking teeth 58 that extend into the slot 52. The locking teeth 58 define a beveled leading edge 60 that that is configured to cam over complementary beveled leading edges 49 of the locking teeth 48 when the strap 32 is translated through the slot 52 along the direction of Arrow A. The locking teeth 58 and 48 further define trailing edges 62 and 47 that are sloped less than the beveled leading edges 60, such that the trailing edges 62 and 47 engage to prevent the strap 32 from translating through the slot 52 along the direction opposite Arrow A, which would increase the size of the loop 55.

During operation, the strap 32 is wrapped around the first and second segments 26 a and 26 b of the target bone 28, and the needle tip 36 is inserted through the slot 52 and pulled through the slot 52 so as to cause the strap 32 to subsequently translate through the slot 52. The needle tip 36 can be removed from the strap 32, and the strap 32 can then be further pulled, for instance manually, through the slot 52. As the strap 32 is translated through the locking mechanism 38 along the direction of Arrow A, the small protrusions of the initiation region 40 can slide through the slot 52 without engaging the locking teeth 58 of the locking mechanism 38. As the locking region 42 of the strap 32 is translated through the slot 52 along the direction of Arrow A, the locking teeth 48 and 58 can engage to prevent the tension that is induced in the strap 32 from causing the strap 32 to back out of the slot 52 along a direction opposite Arrow A. For instance, as the strap 32 translates through the locking mechanism 38 along the direction of Arrow A, the size of the loop 55 about the target bone 28 decreases until tactile feedback indicates that tension has been induced in the strap 32.

As illustrated in FIG. 3B, the fixation instrument 22 includes a tension assembly 70 that is configured to secure the fixation instrument 22 to the strap 32, and is further configured to further pull the strap 32 through the locking mechanism 38 thereby further inducing tension in the strap 32 until the strap 32 has securely compressed the bone first and second bone segments 26 a and 26 b of the target bone 28 together at the fracture location 30. As illustrated in FIG. 3C, the fixation instrument 22 further includes a cutter assembly 72 that is configured to cut a free end 35 of the strap 32 that has passed through the locking mechanism 38 once a desired tension has been induced in the strap 32 about the first and second segments 26 a and 26 b of the target bone 28. For instance, the desired tension can be within a range defined by and between a lower end that can be approximately 50 Newtons or approximately 80 Newtons, and an upper end that can be approximately 150-160 Newtons or 200 Newtons. It should be appreciated that the desired tension can depend on the bone quality and the preference of the surgeon, and can for instance be any tension as desired that reliably secures the target bone 28 without overtightening the strap 32.

Referring now to FIGS. 1 and 4, the fixation instrument 22 includes a body 76 that defines a front end 78 a and an opposed rear end 78 b spaced from the front end 78 a along a longitudinal direction L and opposed sides 80 that are spaced along a lateral direction A that is substantially perpendicular with respect to the longitudinal direction L. The fixation instrument 22 further includes a handle 82 that is supported by the body 76, and can extend down from the body 76 along a transverse direction that is substantially perpendicular with respect to both the longitudinal direction L and the lateral direction A. In accordance with the illustrated embodiment, the transverse direction T is oriented vertically, and the longitudinal and lateral directions L and A are oriented horizontally, though it should be appreciated that the orientation of the fixation instrument may vary during use. In accordance with the illustrated embodiment, the body 76 is elongate in the longitudinal direction L.

The fixation instrument 22 further includes a trigger 84 that extends down from the body 76 at a location spaced forward from the handle 82, and a nose 86 disposed at the front end 78 a of the body 76. The handle 82, the trigger 84, and the nose 86 can be discreetly attached to the body 76 or integral with the body 76 as desired. The body 76 can include an outer housing 88 that includes a pair of housing members 90 a and 90 b that are laterally opposed and define respective outer sides 92 and can be joined together via fasteners such as screws 94 so as to support the various internal components of the fixation instrument 22.

It should be appreciated that the body 76 of the fixation instrument 22 can be constructed in any suitable manner as desired. For instance, as illustrated in FIG. 1, the outer hosing members 90 a and 90 b can include a flange 93 that extends laterally inward toward each other from the sides 80 at a forward location of the body 76. Alternatively, as illustrated in FIG. 10, the flange 93 can extend further rearward and terminate adjacent an actuator 100.

For instance, the housing 88 can support the tension assembly 70 that is configured to tighten the bone fixation member, thereby inducing tension in the bone fixation member 24, such as the strap 32, and can further support the cutter assembly 72 that is configured to remove a free end 35 of the bone fixation member 24 once the tension assembly 70 has induced a desired level of tension in the bone fixation member 24. The tension assembly 70 includes a grip 96 that is movable between a disengaged position (FIG. 7A) whereby the grip 96 is configured to loosely receive the strap 32, such as the portion of the strap that has passed through the locking mechanism 38, and an engaged position (FIG. 7B) whereby the grip 96 is configured to be secured to the received strap 32. The tension assembly 70 further includes a traveler 98 that is operably coupled to the grip 96 and extends rearward from the grip 96, such that rearward movement of the traveler 98 causes the grip 96 to move rearward in the secured configuration, thereby inducing tension in the strap 32. The tension assembly 70 can further include an actuator 100 such as the trigger 84 and a tension limiter 102 (FIG. 6) connected between the trigger 84 and the traveler 98. The tension assembly 70 can further include a force transfer member 104 that is connected between the trigger 84 and the tension limiter 102, thereby operatively coupling the trigger 84 to the traveler 98.

During operation, and as described in more detail below, the free end 35 of the strap 32 is received in the grip 96, the nose 86 is placed against the housing 50 of the locking mechanism 38, and the actuator 100 is moved from an first initial position to a second grip position that causes the grip 96 to iterate from the disengaged position to the engaged position, and is further moved from the second grip position to a third tension position that causes the traveler 98 to move rearward, thereby inducing tension in the strap 32 when the tension in the strap 32 is less than a select tension, which can be a desired maximum tension as determined by the tension limiter 102. When the tension in the strap 32 reaches the maximum tension, the tension limiter 102 prevents the traveler 98 from moving rearward when the actuator 100 is moved to the tension position.

The cutter assembly 72 includes a cutter arm 106 movably supported by the body 76 and a cutter blade 108 that is carried by the cutter arm 106. The cutter arm 106 is movable from a seated disengaged position (see FIG. 4) whereby the cutter blade 108 is spaced from the free end 35 of the strap 32 that is received in the grip 96 to an engaged position (see FIGS. 5A-B) whereby the cutter blade 108 cooperates with a complementary cutter blade 87 of the nose 86 so as to cut the free end 35 of the strap 32 (see FIG. 9). The fixation instrument 22, and in particular the cutter assembly 72, further includes a safety mechanism 110 that moves from a disengaged position, whereby the cutter arm 106 can move from the seated disengaged position toward the engaged position, and an engaged position that prevents the cutter arm 106 from moving from the seated disengaged position toward the engaged position.

Referring now to FIGS. 4 and 7A-B, the traveler 98 of the fixation instrument 22 can be provided as a longitudinally extending traveler rod 111 that extends forward from the tension limiter 102 and supports the grip 96 at its front end. The traveler rod can define a rectangular cross-section as illustrated in FIG. 4, a substantially circular cross section as illustrated in FIG. 10, or any alternative size and shape as desired. The grip 96 includes a first lower grip member 112 and a second upper grip member 114 spaced from the lower grip member 112 so as to define a gap 116 disposed between the lower and upper grip members 112 and 114. The lower grip member 112 defines first grip surface 118 that faces the upper grip member 114, and can further define a plurality of teeth 120 that extend out from the first grip surface 118 toward the upper grip member 114. The teeth 120 are configured to assist in reliably securing the grip 96 to the strap 32. The upper grip member 114 is supported by the traveler rod 111 and defines a second grip surface 115 that faces the first grip surface 118. The first and second grip surfaces 118 and 115 can be sized and shaped as desired. In accordance with the illustrated embodiment, the first grip surface 118 is curved and substantially arc-shaped in accordance with the illustrated embodiment, such that the first grip surface 118 is convex with respect to the upper grip member 114. Furthermore in accordance with the illustrated embodiment, the second grip surface 115 is substantially flat.

The traveler rod 111 defines a forked first front end 117 a that defines a pair of laterally spaced side walls 122. The upper grip member 114 can be rigidly supported by the traveler rod 111, and the lower grip member 112 can be pivotally coupled to the traveler rod 111 at a pivot location 113 about a laterally extending pivot pin 115 that defines a lateral pivot axis, and can further be disposed between the side walls 122. The grip 96 can further include a biasing member such as a torsion spring 124 that biases the lower grip member to pivot in a forward direction about the pivot location 113 toward the nose 86 from the disengaged position of the grip 96 to the engaged position of the grip 96. The grip surface 118 can extend eccentrically about the pivot location 113 such that the grip surface 118 moves upward toward the upper grip member 114 as the lower grip member 112 pivots forward to the engaged position.

The lower grip member 112 defines a first or forward stop surface 126 and the nose 86 defines a complementary second or rear stop surface 127. When the traveler rod 111 is in a forward position, the grip 96 is in the disengaged position whereby the torsion spring 124 biases the forward stop surface 126 against the rear stop surface 127. When the grip is in the disengaged position, the gap 116 is sized greater than the thickness of the free end 35 of the strap 32 as illustrated in FIG. 7A. Accordingly, the free end of the strap 35 can be received in the gap 116 between the first and second grip surfaces 118 and 115 as illustrated in FIG. 8A. As the traveler rod 111 moves rearward, the lower grip member 112 pivots forward about the pivot location 113 such that the grip surface 118 moves toward the grip surface 115 of the upper grip member 114 as illustrated in FIG. 7B, thereby reducing the gap 116 until the grip 95 captures the free end 35 of the strap 32 that is received in the gap 116 between the first and second grip surfaces 118 and 115 under the force of the torsion spring 124 (FIG. 8B). It should thus be appreciated that as the traveler rod 111 further moves rearward, the free end 35 of the strap 32 will move rearward along with the grip 95 and the traveler rod 111.

Referring now to FIGS. 4 and 6, the traveler rod 111 defines a second rear end 117 b opposite the front end 117 a. The rear end 117 b of the traveler rod 111 is connected to the tension limiter 102. The tension limiter 102 includes a spring member 128 such as a helical compression spring that defines a first or front end 130 a and a second or rear end 130 b. The spring member 128 is fixed with respect to movement relative to the traveler rod 111 at its rear end 130 b, and movable with respect to the traveler rod 111 at its front end 130 a. The spring member 128 is further coupled to the trigger 84 at its front end. Thus, the spring member 128 is coupled to the trigger 84 at its end that is also movable with respect to the traveler rod 111 so as to generate a force to the traveler rod 111 that biases the traveler rod rearward away from the locking mechanism 38 of the bone fixation member 24.

In accordance with the illustrated embodiment, the tension limiter 102 includes a stationary end cap 129 that can be threaded onto or otherwise secured to the traveler rod 111, for instance to the rear end 117 b of the traveler rod 111. The rear end 130 b of the spring member 128 is attached to the end cap 129 so as to secure the spring member 128 to the traveler rod 111 at its rear end 130 b such that the rear end 130 b is fixed with respect to movement relative to the rod 111. Thus, as the rear end 130 b of the spring member 128 moves rearward, the traveler rod moves rearward along with the rear end 130 b of the spring member 128. The tension limiter 102 can further include a movable spring seat 132 that is fixed to the movable front end 130 a of the spring member 128. In accordance with the illustrated embodiment, the traveler rod 111 extends through the spring seat 132, such that the spring seat 132 is movable in the longitudinal direction L along the traveler rod 111. The traveler rod 111 can define a longitudinally elongate slot 134 extending therethrough that can receive a projection of the spring seat 132. Thus, the slot 134 defines a length that allows the movable spring seat 132 to translate from its forward-most position to its rearward-most position.

The tension assembly 70 further includes the force transfer member 104 illustrated as a force transfer arm 136 that is pivotally connected between the movable spring seat 132 and the trigger 84. Otherwise stated, the movable front end 130 a of the spring member 128 is coupled to the trigger 84 via the force transfer arm 136. In accordance with the illustrated embodiment, the force transfer arm 136 defines a front end 138 a and an opposed rear end 138 b. The force transfer arm 136 is pivotally coupled, for instance at its rear end 138 b to the spring seat 132 at a pivot location 139 that defines a lateral pivot axis. The force transfer arm 136 is further pivotally coupled, for instance at its front end 138 a to the trigger 84 at a pivot location 140 that defines a lateral pivot axis.

Referring again to FIG. 4, tension assembly 70 further includes the trigger 84 that includes a lower grip portion 85 extending down from the housing 88 at a location spaced forward of the handle 82 and an upper securement portion 89 pivotally connected to the force transfer arm 136 and further pivotally connected to the housing 88. The trigger 84 defines an aperture 91 that extends longitudinally through the upper securement portion 89 and receives the traveler rod that extends through the aperture, and thus the upper securement portion 89. The securement portion 89 of the trigger 84 is pivotally connected to the force transfer arm 136 at the pivot location 140, which defines a first lower pivot location of the trigger 84. The securement portion 89 of the trigger 84 is further pivotally coupled to the housing 88 at a second upper pivot location 142 that defines a lateral pivot axis. The user can grasp the handle 82 and the grip 85 of the trigger 84 with one hand, and squeeze the trigger 84, which causes the trigger 84 to pivot rearward about the second upper pivot location 142. Because the lower pivot location 140 is disposed between the upper pivot location 142 and the grip 85, the lower pivot location 140 moves rearward when the trigger 144 is moved rearward by the user. The tension assembly 70 further includes a spring member 146 that is connected between the handle 142 and the trigger 144 that biases the trigger 144 forward to its initial position. The fixation instrument 22 includes a stop member illustrated as a dowel 148 that extends laterally between the housing members 90 a and 90 b. The front edge of the securement portion 89 of the trigger 84 abuts the dowel 148 so as to locate the trigger 144 in its first initial position under the force of the spring member 146.

Operation of the fixation instrument will now be described with further reference to FIGS. 8A-E. For instance, as illustrated in FIGS. 7A and 8A, the trigger 84, and thus the tension assembly 70, is in a first initial position whereby the front end 117 a of the traveler rod 111 is disposed adjacent and proximate to the nose 86, such that the forward stop surface 126 of the lower grip member 112 abuts the complementary rear stop surface 127 of the nose 86, thereby causing the gap 116 to define a transverse thickness greater than that of the free end 35 of the strap 32. The free end 35 is inserted into the gap 116 and the nose 86 is positioned so as to abut the locking mechanism 38. The nose 86 thus provides a brace member that prevents the locking mechanism 38 from traveling rearward when the fixation instrument 22 applies a rearward force to the free end 35.

When the tension assembly 70 is in the first initial position, the spring member 128 can be in an initial position that can be a neutral position, or the movable spring seat 132 can be disposed at a forward location with respect to the neutral position such that the initial position of the spring member 128 can be flexed, such as slightly extended, from its neutral position. For instance, the force of the spring member 146 that biases the trigger 84 forward can be greater than the force of the spring member 128 that biases the trigger 84 rearward when the movable spring seat 132 is displaced forward from its neutral position. When the spring member 128 is extended from its neutral position, the spring member can apply a rearward compressive force onto the end cap 129, and thus the traveler rod 111, which biases the lower grip member 112 forward against the nose 86. It is appreciated that the torsion spring 124 that biases the lower grip member 112 forward against the nose 86 creates an equal and opposite force against the traveler rod 111 that biases the traveler rod rearwards. Thus, the forward force of the spring member 128 applied to the traveler rod 111 when the spring member 128 is slightly extended is greater than the rearward biasing force of the torsion spring 124 against the traveler rod 111. Because the forward biasing force of the spring member 128 is greater than the rearward biasing force of the torsion spring 124 when the spring member 128 is slightly extended, the spring member 128 can actively maintaining the grip 96 in its disengaged position.

Alternatively, the movable spring seat 132, and thus, the spring member 128, can be in a neutral position when the tension assembly 70 is in the first initial position, such that the spring member 128 does not apply a forward biasing force or a rearward biasing force to the traveler rod 111. As described above, the torsion spring 124 can apply a force to the traveler rod 111 that biases the traveler rod rearwards 111. However, rearward movement of the traveler rod 111 would cause the rear end 130 b of the spring member 128 to move away from the front end 130 a of the spring member 128, thereby causing the spring member 128 extend from its neutral position. The spring member 128 can have an spring constant that is greater than the spring constant of the torsion spring 124 such that the spring member 128 resists extension under the forces of the torsion spring 124, and thereby passively maintains the lower grip member 112 in its disengaged position whereby the forward stop surface 126 rests against the complementary rear stop surface 127 of the nose 86 and the gap 116 is thus thicker in the transverse direction T than the free end 35 of the strap 32 that is received in the gap 116.

Referring now to FIGS. 4 and 8B, when the user applies a rearward directed force F to grip portion 85 of the trigger 84, the trigger 85 and thus also the tension assembly 70 moves from the first initial position to the second grip position that causes the grip 96 to iterate from the disengaged position to the engaged position. In accordance with the illustrated embodiment, the rearward force applied to the grip portion 85 of the trigger 84 causes the trigger 84 to pivot rearward about the upper pivot location 142, which causes the lower pivot location 140 to move rearward. It should be appreciated that the lower pivot location 140 moves rearward about an arc-shaped travel path about the upper pivot location 142. Rearward movement of the lower pivot location 140 causes the force transfer arm 136 to likewise moves rearward, thereby transferring the force from the trigger to the movable spring seat 132 and the front end 130 a of the spring member 128. It should be appreciated that the force transfer arm 136 pivots relative to the trigger 84 about the lower pivot location 140 as the force transfer arm 136 moves rearward.

As the force transfer arm 136 moves rearward, the force transfer arm 136 further causes the movable spring seat 132 and the front end 130 a of the spring member 128 to translate rearward along the travel rod 111 in the longitudinal direction L toward the rear end 130 b of the spring member 128, thereby flexing the spring member 128 from the first initial position. It should be appreciated that the force transfer arm 136 pivots relative to the movable spring seat about the pivot location 139. As the front end 130 a of the spring member 128 moves rearward toward the rear end 130 b of the spring member 128, the spring member 128 flexes from its neutral position so as to apply a rearward biasing force to the traveler rod 111. In accordance with the illustrated embodiment, the spring member 128 compresses when the end 130 a of the spring member 128 moves rearward, and thus biases the end 130 b, the end cap 129, and also therefore the traveler rod 111 to move rearward. Alternatively, the movement of the end 130 a of the spring member 128 can be sufficient so as to reduce the force of the spring 128 that biases the traveler rod 111 to a level that is less than the force of the torsion spring 124 that biases the traveler rod 111 rearward. The fixation instrument 22 can define an aperture 119 that extends through the rear end 78 b of the body 76. The aperture 119 is sized to receive the end cap 129 such that the end cap 129 can extend beyond the housing 88 due to rearward travel of the rear end 130 b of the spring member 128.

Accordingly, referring also to FIGS. 7A-B, the traveler rod 111 is biased, under a biasing force applied by the torsion spring 124, the spring member 128, or both to move rearward away from the nose 86. As the rod 111 moves away from the nose 86, the torsion force of the torsion spring 124 causes the lower grip member 112 to pivot forward about the pivot location 113 along the direction of Arrow B so as to reduce the gap 116 until the grip surfaces 118 and 115 capture the free end 35 of the strap 32 in the gap 116, thereby securing the free end 35 to the fixation instrument 22 while the nose 86 abuts the loop 55, and in particular the housing 50 of the locking mechanism 38. Thus, it can be said that moving the trigger 84 from the first neutral position to the second neutral position causes the grip 96 to iterate from its disengaged position to its engaged position

Referring now to FIGS. 4, 6, and 8C, continuous application of the force F to the grip portion 85 of the trigger 84 causes the trigger 84 to further pivot about the upper pivot location 142, thereby causing the trigger 84, and thus the tension assembly 70, to move from the second grip position to a third tension position that causes the traveler 98 to move rearward, thereby applying tension to the free end 35 of the strap 32 when the tension in the strap 32 is less than the desired tension, such as a maximum tension as determined by the tension limiter 102. Because engagement of the nose 86 of the fixation instrument 22 with the loop 55, and in particular the housing 50 of the locking mechanism 38, provides a brace that prevents the loop 55 from moving rearward along with the free end 35, when the tension assembly 70 places the free end 35 in tension, the strap 32 and in particular the locking region 42 is further pulled through the locking mechanism 38. As described above with reference to FIG. 2B, the locking teeth 58 and 48 engage so as to allow the locking region 42 to be pulled through the locking mechanism so as to reduce the size of the loop 55 or to place the loop 55 in further tension about the bone segments that are disposed in the loop 55. Whether the size of the loop 55 is reduced or whether the loop 55 is further tightened about the bone segments disposed in the loop, it can be said that the fixation instrument places the bone fixation member 24 in tension when the tension assembly moves from the second grip position to the third tension position.

Accordingly, once a trigger stroke has been completed whereby the trigger 84 has been moved to its rearward-most position as illustrated in FIG. 8C, the user can release the trigger 84 which causes the spring member 146 to bias the trigger 84 to its forward position shown in FIG. 8D. Once the trigger 84 has moved to its forward position, the trigger 84 and thus the tension assembly 70 are in the first initial position, such that the lower grip member 112 is biased against the nose 86 thereby placing the grip 96 in its disengaged position as described above. Accordingly, while the free end 35 of the strap 32 is no longer secured to the fixation instrument 22, the engagement of the locking teeth 58 and 48 prevent the increased tension induced in the loop 55 from allowing the free end 35 to move through the housing in a direction opposite Arrow A that would reduce the tension in the loop 55.

It should be appreciated that the motion of the trigger 84 from the second grip position to the third tension position can be a continuation of the movement from the first initial position to the second grip position. Thus, the trigger 84 can move from the first initial position to the second grip position to the third tension position in a single fluid motion.

The nose 86 can again be placed in contact with the locking mechanism 38 and the free end 35 can be received in the gap 116 of the grip 96, and the tension assembly 70 can be iterated from the first initial position to the second grip position to the third tension position as many times as desired, for instance until the tension induced in the loop 55 reaches a predetermined maximum tension. When the tension in the loop 55 reaches the maximum tension, the tension limiter 102 prevents the traveler 98 from moving rearward when the actuator 100 is moved to the tension position.

For instance, referring now to FIGS. 4, 6, and 8E, it should be appreciated that the spring member 128 has a spring constant that is configured to apply a predetermined biasing force to the traveler rod 111 when the front end 130 a of the spring member 128 has translated rearward a distance corresponding to full rearward actuation of the trigger 84. Accordingly, so long as the tension in the loop 55 is less than the desired force as defined by the spring member 128 and length of travel of the front end 130 a of the spring member 128, compression of the spring member 128 will cause the force applied by the spring member 128 to move the traveler rod 111 rearwards. However, once the tension induced in the loop 55 reaches the desired force, compression of the spring member 128 due to rearward movement of the front end 130 a will cause the spring member 128 to apply a rearward biasing force against the traveler rod 111 that is insufficient to overcome the force necessary to further tighten the loop 55.

It should appreciated that the spring member 128 can be configured to apply a rearward biasing force against the traveler rod 111 that is greater than the tension induced in the loop 50 about the target bone 28. For instance, the spring member 128 can apply a force that is sufficient to overcome both the tension of the loop 50 and the additional force that causes one or both of the locking teeth 48 and 52 to deflect as the teeth ride over each other when tightening the loop 55. Accordingly, the tension limiter 102 can be configured apply a force that is greater than, but corresponds to, the tension in the loop 55 about the target bone. Thus, the maximum force applied by the tension limiter 102 can correspond to the maximum desired tension in the loop 55, it being appreciated that once the teeth 48 and 52 ride over and past each other, the tension in the loop 55 can decrease somewhat as the teeth 48 and 52 interlock. In accordance with one embodiment, the tension limiter 102 can apply a maximum force as desired, for instance up to approximately 430 Newtons or any other force as desired that corresponds to a desired maximum tension in the loop 55 about the target bone 28. As a result, once the desired maximum tension in the loop 55 has been induced about the target bone 28, the force applied by the tension limiter 102 when the trigger 84 is fully actuated is insufficient to cause the teeth 48 and 58 to ride past each other and further tighten the loop 55. Accordingly, once the maximum tension in the loop 55 has been induced about the target bone 28, the force applied by the tension limiter 102 will be insufficient to cause the traveler rod 111 to translate rearward a sufficient distance that further tightens the loop 55 about the target bone 28.

It should be appreciated that the spring member 128 can alternatively be configured as an extension spring. For example, in accordance with an alternative embodiment, the front end 130 a can be connected to the traveler rod 111 and fixed with respect to the traveler rod 111, and the rear end 130 b can be movable relative to the traveler rod 111. For instance, the rear end 130 b can be coupled to the trigger 84 via the force transfer member 104 in the manner described above. The tensile force applied to the rear end 130 b and corresponding rearward displacement of the rear end 130 b can thus cause the spring force to bias the traveler rod 111 to move rearward, thereby inducing tension in the strap 32 in the manner described above. Thus, the initial position of the spring member 128 initial position that can be a neutral position as described above, or the initial position of the spring member 128 can be flexed, such as slightly compressed, from its neutral position.

Referring now to FIGS. 4-5B, the fixation device 22 includes a cutter assembly 72 that includes a cutter arm 106 having a front end 107 a and a rear end 107 b, and a movable cutter blade 108 carried by the cutter arm 106, for instance at the front end 107 a. The cutter arm 106 can be sized and shaped as desired, and is constructed in accordance with the illustrated embodiment such that the front and rear ends 107 a and 107 b extend substantially longitudinally. The cutter arm 106 can also include an offset segment 107 c that extends laterally outward along a forward direction from the rear end 107 b toward the front 107 a. Thus, the front end 107 a can be offset laterally outward with respect to the rear end 107 b. For instance, the rear end 107 b can be disposed between the opposed sides 80 and the front end 107 a can be coupled to one of the side 80 at a location laterally outward of the side 80. The cutter arm 106 can further include an intermediate longitudinal segment 107 d that extends forward from the offset segment 107 c and is thus extends substantially parallel to the front and rear ends 107 a and 107 b. The cutter arm can also include a transversely offset segment 107 e that extends between the intermediate longitudinal segment 107 d and the front end 107 a, and extends transversely down along a forward direction. Accordingly, the front end 107 a can be transversely offset with respect to the rear end 107 b. The cutter arm 106 can further include a grip 150 at disposed at the rear end 107 b.

Referring also to FIG. 6, the cutter assembly 72 can include a seat 158 that receives the cutter arm 106 at an upper end of the body 76 when the cutter arm 106 is in its disengaged position. In accordance with the illustrated embodiment, the seat 158 is sized and shaped so as to receive the cutter arm 160. Accordingly, when the cutter arm 106 is seated in the seat 158, the cutter arm 106 can be said to be in a seated disengaged position. The seat 158 can further include at least one retainer member 162, such as a pair of laterally opposed retainer members 162 that are spaced apart a distance slightly less than the lateral thickness of the cutter arm 106. The retainer members 162 can be spring loaded to the position spaced apart a distance slightly less than the lateral thickness of the cutter arm 106. For instance, the cutter arm 106 can define a recess 164 that is sized to receive the retainer members 162 when the cutter arm 106 is in its seated disengaged position. Accordingly, when moving the cutter arm 106 to and from its seated disengaged position, an engagement force along the direction of Arrow C can be applied to the cutter arm 106 that is sufficient to overcome the retention force of the retainer members 162, which causes the retainer members 162 to pop out of the recess 164 and free the cutter arm 106 from the seat 158.

Referring also to FIGS. 7A-B, the cutter arm 106 can be pivotally attached to the body 76, for instance at one of the sides 80. In accordance with the illustrated embodiment, the cutter arm 106 is pivotally attached at its front end 107 a to the nose 86 at a pivot location 152 that defines a lateral pivot axis. For instance, the cutter assembly 72 can include a blade support body 154 that is substantially cylindrical and extends through a side wall of the nose 86 and rotatable about its central axis so as to allow the cutter arm 106 to pivot between its engaged position and its disengaged position. When the cutter arm 106 is in its disengaged position, the cutter blade 108 is spaced above a complementary and substantially stationary cutter blade 87 of the nose 86 so as to define a gap 156 that has a transverse dimension greater than that of the free end 35 of the strap 32 so that the free end 35 is loosely received in the gap 156, which is disposed forward with respect to the grip 96, and thus the gap 116.

Referring again to FIGS. 5A-B, the cutter arm 106 can be pivoted up and forward about the pivot location 152 along the direction of Arrow C to its engaged position, which causes the cutter blade 108 to travel down along an arc-shaped path toward the complementary cutter blade 87 so as to reduce the size of the gap 156. The cutter blade 108 is recessed rearward with respect to the complementary cutter blade 87 such that the cutter blade 108 slides past the cutter blade 87. Accordingly, the cutter blades 108 and 87 cooperate so as to cut the free end 35 of the strap 102 that is received in the gap 156 as the cutter blade 108 slides past the cutter blade 87 (see FIG. 9). Accordingly, when the nose 86 abuts the locking mechanism 38 of the bone fixation member 24 such that the gap 156 is aligned with the outlet end of the strap-receiving slot 52 of the housing 50 of the locking mechanism (see FIGS. 2B and 3C) and the arm 106 is moved to its engaged position, the cutter assembly 72 can cut the free end 35 at a location that is spaced from the housing 50 a distance substantially equal to the distance between the front end of the nose 86 and the cutter blade 108. Therefore, once the fixation instrument 22 has applied the desired amount of tension in the strap 32, the free end 35 can be cut in the manner described above to substantially remove the free end 35 from the loop 55.

Referring now to FIGS. 4 and 6, the cutter assembly 72 further includes a safety mechanism 110 that moves from a disengaged position, whereby the cutter arm 106 can move from the seated disengaged position toward the engaged position, and an engaged position that prevents the cutter arm 106 from moving from the seated disengaged position toward the engaged position. In accordance with the illustrated embodiment, the cutter assembly 72 includes a first engagement member 166 that extends down from the cutter arm 106 and a second engagement member 168 that extends up from the movable spring seat 132. When the tension assembly 70 is in the first initial position, the first engagement member 166 is spaced rearward from the movable spring seat 132. Otherwise stated, the first engagement member 166 is spaced from the movable spring seat 132 in the direction that the spring seat 132 moves when the tension assembly 70 is moved from the first initial position toward the third tension position. Accordingly, second engagement member 168 can move toward the first engagement member as the movable spring seat 132 moves rearward. Alternatively, the second engagement member 168 can extend from the traveler rod 111 and movable along with the traveler rod 111 so as to interlock with the engagement member 166.

The first and second engagement members 166 and 168 are configured so as to interlock when they longitudinally overlap. For instance, the second engagement member 168 can be configured as a housing 170 having a slot 172 that receives the first engagement member 166. The first engagement member 166 can define a flange 174 that overlaps the housing 170 in the transverse direction, such that the flange 174 abuts the housing 170 when an engagement force is applied to the cutter arm 106 along the direction of Arrow C so as to move the cutter arm 106 from its seated disengaged position toward its engaged position. In accordance with the illustrated embodiment, the first and second engagement members 166 and 168 interfere so as to prevent the cutter arm 106 from being unseated from the seat 158. It should be appreciated that the first engagement members 166 and 168 can alternatively be sized and shaped as desired so as to selectively interfere with each other in the manner described herein.

Referring also to FIG. 8A, when the tension assembly 70 is in the first initial position, the first and second engagement members 166 and 168 are longitudinally spaced apart such that the cutter arm 106 can be moved from the seated disengaged position to the engaged position along the direction of Arrow C. When the tension assembly 70 moves to the second grip position, the movable spring seat 32 translates longitudinally rearward, thereby also translating the second engagement member 168 longitudinally rearward toward the first engagement member 166. In accordance with the illustrated embodiment illustrated in FIG. 8B, the engagement members 166 and 168 remain longitudinally spaced from each other when the tension assembly 70 is in the second grip position, thereby allowing the cutter arm 106 to become unseated and move from the disengaged position toward the engaged position. Accordingly, referring to FIG. 9, after the fixation instrument 22 has induced a desired amount of tension in the loop 55, the tension assembly 70 can be moved to the grip position so as to capture the free end 35 in the gap 116 prior to cutting the free end 35 in the manner described above. Thus, as illustrated in FIG. 3A, the plurality of bone fixation members 24 can be tightened about the target bone 28 by actuating the tension assembly 70 as described herein, and can be subsequently cut by actuating the cutter assembly 72 as described herein.

In accordance with the illustrated embodiment shown in FIG. 8C, the engagement members 166 and 168 are positioned so as to overlap when the tension assembly 70 has moved from the second grip position toward the third tension position. Thus, once the tension assembly 70 has advanced beyond the second grip position, the engagement members 166 and 168 interfere when the engagement force is applied to the cutter arm 106 along the direction of Arrow C. Therefore, the safety mechanism 110 prevents the fixation instrument 22 from cutting the free end 35 while the tension assembly 70 is applying tension to the strap 32. Alternatively, the engagement members 166 and 168 can be positioned so as to at least partially overlap and interlock when the tension assembly 70 is in the second grip position, thereby defining an interference that prevents the cutter arm 106 from becoming unseated and moving to the engagement position along the direction of Arrow C.

Although the disclosure has been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present disclosure is not intended to be limited to the particular embodiments described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, composition of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present disclosure. 

What is claimed:
 1. A bone fixation instrument configured to apply tension to a bone fixation member so as to tighten the bone fixation member about a target bone, the fixation instrument comprising: a body defining a front end and an opposed rear end that is spaced from the front end along a longitudinal axis; a grip configured to secure a free end of the fixation member to the fixation instrument, a traveler that is connected to the grip such that the grip moves rearward along with the traveler so as to increase tension in the bone fixation member; wherein the grip is movable between a disengaged position and an engaged position, such that when the grip is in the disengaged position, the grip defines a gap sized to receive the bone fixation member, and when the grip is in the engaged position, the gap is reduced such that the grip secures the bone fixation member to the bone fixation instrument; wherein the grip member moves from the disengaged position to the engaged position when the traveler moves rearward from a forward position; and, wherein the grip member moves from the engaged to the disengaged position when the traveler returns to the forward position, such that the free end of the fixation member is no longer secured to the fixation instrument; an actuator operatively coupled to the traveler, the actuator configured to move from an initial position toward a tension position in response to an applied force, thereby biasing the traveler to move rearward; and a tension limiter operatively connected between the actuator and the traveler, wherein the tension limiter allows the traveler to move rearward when the tension in the bone fixation member is less than a select tension, and prevents the traveler from moving rearward when the tension in the bone fixation member reaches the select tension, and, wherein the traveler and the tension limiter are oriented substantially along the longitudinal axis of said body.
 2. The bone fixation instrument as recited in claim 1, wherein the grip further comprises first and second grip members, such that one of the grip members is movable between a disengaged position and an engaged position, such that the movable grip member is spaced apart further from the other grip member in the disengaged position than in the engaged position.
 3. The bone fixation instrument as recited in claim 2, wherein the movable grip member is biased toward the engaged position and engages the body so as to prevent the movable grip member from moving from the disengaged position to the engaged position when the traveler is in the forward position.
 4. The bone fixation instrument as recited in claim 3, wherein when the traveler moves rearward from the forward position, the movable grip member becomes disengaged from the body and is biased to the engaged position.
 5. The bone fixation instrument as recited in claim 1, wherein the tension limiter comprises a spring member operatively connected between the actuator and the traveler, wherein movement of the actuator causes the spring member to flex and bias the traveler rearward under a biasing force.
 6. The bone fixation instrument as recited in claim 5, wherein the actuator is movable from the initial position to a second position that causes the spring to flex to a position that biases the traveler rearward and causes the grip to secure to the bone fixation member prior to increasing the tension in the bone fixation member.
 7. The bone fixation instrument as recited in claim 5, wherein the spring compresses as the actuator moves from the initial position toward the tension position, and the compression of the spring causes the spring to bias the traveler to move rearward.
 8. The bone fixation instrument as recited in claim 5, wherein the traveler moves rearward when the biasing force is greater than the tension in the bone fixation member.
 9. The bone fixation instrument as recited in claim 8, wherein the traveler remains stationary when the biasing force is not greater than the tension in the bone fixation member.
 10. The bone fixation instrument as recited in claim 5, further comprising a force transfer member coupled between the actuator and the spring member, wherein movement of the actuator moves the force transfer member to flex the spring member.
 11. The bone fixation instrument as recited in claim 10, wherein the spring member is coupled to a movable spring seat that is connected to the force transfer member.
 12. The bone fixation instrument as recited in claim 1, wherein the actuator is movable from the initial position to a second position that causes the grip to secure to the bone fixation member, and from the second position to the tension position that causes the traveler to move and increase the tension in the bone fixation member.
 13. The bone fixation instrument as recited in claim 12, wherein the actuator moves from the initial position to the second position to the tension position in one continuous motion.
 14. The bone fixation instrument as recited in claim 1, further comprising a cutter assembly configured to move from a disengaged position to an engaged position, whereby the cutter assembly cuts the free end of the bone fixation member when in the engaged position.
 15. The bone fixation instrument as recited in claim 14, further comprising a safety mechanism that prevents the cutter assembly from moving from the disengaged position to the engaged position when the traveler has moved rearward so as to increase tension in the bone fixation member.
 16. The bone fixation instrument as recited in claim 14, wherein the grip and the cutter assembly are both substantially aligned along the same axis as the traveler.
 17. A bone fixation system comprising: at least one bone fixation member including a strap and a locking mechanism, wherein the strap can be pulled through the locking mechanism along a first direction so as to form a loop about a target bone, and the locking mechanism prevents the strap from moving therethrough along a second direction opposite the first direction, wherein the strap defines a free end that extends out the locking mechanism; and a bone fixation instrument configured to apply tension to the loop about the target bone, the fixation instrument including: a tension assembly configured to secure the free end to the fixation instrument, and further configured to pull the free end so as to increase tension in the loop while the tension in the loop is less than a select tension, wherein the tension assembly is unable to further increase tension in the bone fixation member once the tension in the bone fixation member has reached the select tension; a tension limiter for setting the select tension and for preventing the tension assembly from further increasing tension in the bone fixation member once the tension therein has reached the select tension by applying a force that counteracts the tension applied by the tension assembly; and a cutter assembly that is configured to cut the free end of the bone fixation member so as to separate the free end from the loop by moving from a disengaged position to an engaged position independently of whether the tension in the bone fixation member has reached the select tension.
 18. The bone fixation system as recited in claim 17, wherein the tension assembly further comprises a grip that is configured to move from 1) a disengaged position wherein the grip is configured to loosely receive the free end of the bone fixation member to 2) an engaged position wherein the grip secures the free end of the bone fixation member to the bone fixation instrument, and, wherein the grip and the cutter assembly are both substantially aligned along the longitudinal axis of the fixation instrument.
 19. The bone fixation system as recited in claim 17, wherein said tension limiter comprises a spring element. 